1. Technical Field
The present invention relates to a fuel injection control device which corrects a suction air amount signal erroneously measured in association with pulsation of suction air during acceleration or deceleration of an engine.
2. Description of the Prior Art
A Karman's vortex type flow meter is known as a means for measuring fluid flow (Japanese Patent Publication No. 51-13428). The Karman's vortex type flow meter has relatively many advantages in that the flow measuring response to a change in flow is good and the fluid resistance in a passage is small as compared with a vane type flow meter.
In an internal combustion engine having a Karman's vortex type flow meter in a suction passage, the number of Karman's vortices generated in proportion to the amount of suction air is detected by ultrasonic modulation, and the amount of fuel to be injected from a fuel injector is computed according to a measured value of suction air amount as measured by the number of Karman's vortices Japanese Patent Publication No. 60-10171).
Concretely, a columnar Karman's vortex generating device is provided in the suction passage to drive a pulse generator for generating a fixed pulse according to Karman's vortex generated downstream of the device, thereby supplying fuel in the amount proportional to an output frequency of the pulse generator.
A hot-wire type flow meter is known as another type of suction air amount measuring means. In engines employing a hot-wire type flow meter, a predetermined current flows in a platinum hot wire, for example, provided in the suction passage, and the amount of suction air is measured according to the amount of change in resistance of the platinum hot wire cooled by the suction air passing through the hot wire. Then, the amount of fuel as determined according to the measured amount of the suction air is supplied to the engine.
The Karman's vortex type flow meter and the hot wire type flow meter as mentioned above are provided in the suction passage which is regarded as a substantially mere cylinder.
As is mentioned above, the suction passage including the conventional Karman's vortex type flow meter or hot-wire type flow meter is formed cylindrically. Therefore, in an internal combustion engine having such suction air amount measuring means in the cylindrical suction passage, measurement of the amount of suction air is apt to be influenced by pulsation of the suction air, particularly just after rapid closing or rapid opening of a throttle valve at rapid deceleration or rapid acceleration when the suction air pulsates largely. As a result, a frequent problem is that the amount of suction air to be detected by the aforementioned flow meters is not properly measured during a transitional operation.
As a result, an error is apt to be created in the amount of fuel to be injected as computed according to the suction air amount signal during the transitional operation to cause over-richness or over-leanness of fuel.